In situ combustion method for high viscosity petroleum deposits



Aug. 2, 1966 W. C. HARDY IN SITU COMBUSTION METHOD FOR HIGH Filed May 23, 1963 VISCOSITY PETROLEUM DEPOSITS 2 Sheets-Sheet 1 INVENTQR. WILLIAM C. HARDY ATTORNEYS Aug. 2, @966 w. c. HARDY IN SITU COMBUSTION METHOD FOR HIGH VISCOSITY PETROLEUM DEPOSITS 2 Sheets-Sheet 2 Filed May 23, 1 963 wmswmwmm TEMPERATURE FIG. 4.

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ATTORNEYS United States Patent 3,263,750 IN SITU COMBUSTION METHOD FOR HIGH VESCOSITY PETROLEUM DEPOSITS William C. Hardy, Richardson, Tex., assignor to Sun 011 Company, Philadelphia, Pa., a corporation of New Jersey Filed May 23, 1963, Ser. No. 282,632 Claims. (Cl. 16611) This invention relates to a method for recovery of hydrocarbons from oil-bearing formations, and has particular reference to recovery processes involving in situcombustion.

Recovery of hydrocarbons by the use of in situ combustion procedures is known, there being two classes of such procedure involving, respectively, forward or backward burning. The present invention is concerned with the forward burning procedure.

In carrying out this procedure, the petroleum-bearing formation from which recovery is sought is penetrated by one or more injection wells and one or more production wells suitably drilled in what appears from prior knowledge of the formation to be optimum locations. The procedure involves injection of air into the injection well or wells, the initiation and maintenance of burning starting at the injection point, and the collection of the resulting product from the producing well or wells. Particular procedures for carrying this out are well known and need not be described in detail. The combustion process is used usually as a secondary recovery process but may be used when other procedures have failed either to initiate or continue production. For example, due to its geologic history, some beds, e.g., tar sands, may, when first located, contain only, or largely, highly viscous and non-volatile hydrocarbon residues which cannot be made to flow by ordinary methods. In other cases, more conventional methods may have been used to remove more mobile and volatile constituents leaving residually in the formation pores residues which are so viscous as not to flow or which are in such quantities as to be held by wetting of the rock constituents without existing in a continuous liquid phase. To attack these or similar conditions, the burning process is used, which, consuming some of the hydrocarbon residues, provides heat which cracks other portions of the residues producing gaseous and/or liquid products which will flow to the production point.

While, as will become apparent, the present invention is applicable to the in situ combustion treatment of other types of reservoirs, it is particularly applicable to the recovery of low gravity, high viscosity, high boiling point oils or bitumens from underground strata in which they occur. In such a case there are produced as sub zones flanking a central portion of a condensation zone which have high oil saturations which interfere with proper progress of the combustion recovery operation. These sub zones depend upon the distillation characteristics of the crude oil. Briefly stated, it is the general object of the present invention to effect modification of these sub zones to promote the desired recovery. In the following description, the factors involved will be considered in greater detail, and the achievement of the broad and specific objectives of the invention will become more apparent with reference to the accompanying drawing in which:

FIGURE 1 is a diagram, in the form of a vertical section illustrating a portion of an oil reservoir to which the invention is applied;

FIGURE 2 is a plot of temperature versus distance, to the horizontal scale of FIGURE 1, explanatory of the type of problem which exists and which it is the object of the present invention to solve;

FIGURE 3 is a plot similar to FIGURE 2 illustrating the modifications effected in accordance'with the present invention;

FIGURE 4 is a liquid-vapor phase diagram of static pressure plotted against temperature for a typical 'hydrocarbon composition originally found in a reservoir to be treated in accordance with the present invention; and

FIGURE 5 is a similar phase diagram illustrative of modifications effected in accordance with the invention.

Referring first to FIGURE 1, one or more injection wells are indicated at 2, provided with control valves 4, and penetrating at their lower end 6 a hydrocarbon-containing formation indicated at 8. Spaced from these -are producton wells 10 illustrated as provided with control valves 12, which wells penetrate the same formation at 14. It will be understood that while these wells are merely diagrammed, they may be provided in accordance with well-known practices which need not be described in detail, having no bearing on the essential aspect of the invention. The production wells may, of course, be pumped if required. The wells are also relatively located in accordance with conventional good practices depending upon the knowledge of the producing formation, this knowledge being secured by preliminary conventional production, by the drilling of test holes with core sampling, etc. In brief, the arrangement adopted is to secure, ultimately, maximum recovery with minimum cost. It might be stated, as a summary, that the locations are such as to secure a-sweeping of desired products from a maximum region consistent with the adoption of the forward burning procedure.

Considering the Wells indicated in FIGURE 1, the formation between the injection well or wells and the production Well or wells, contains identifiable zones though the boundaries of transition from each zone to the next may not be sharply defined; in fact they may be quite indefinite.

From the standpoint of consideration of the present invention, the zones which would exist in the ordinary forward combustion procedure after burning had occurred to some extent would be as generally illustrated in FIGURE 2. First, in the vicinity of the injection well or wells there would be a burned zone indicated at 16. Following this, in the direction of flow, is a combustion zone indicated at 18. Immediately following this, there is a cracking zone in which high temperatures exist and which, so far as the present invention is concerned, need not be differentiated but may be considered as part 20 of the combustion zone. Following this is the condensation zone indicated at 22. This involves a steeptemperature gradient region followed by a plateau and then another higher temperature gradient region joining the condensation zone with what may be considered the ambient or unaltered zone 24. The initial portion of this latter may involve a gas solution subzone, but for consideration of the present invention this subzone may be considered as part of the unaltered zone. It is the condensation zone 22 which is of particular concern in connection with the matters of the present invention.

Considering, now, what would ordinarily occur in the combustion operation involving a reservoir containing low gravity, high viscosity, high boiling point oils or bitumens, the magnitude of the temperatures in the zones mentioned depends upon the particular conditions of pressure and composition of the reservoir rock and contained petroleum oil. The temperatures generally fall within the following ranges:

In the burned zone, depending upon the extent to which the burning operation has been carried out, the temperatures may range upwardly from an ambient temperature (resulting from cooling by injected air) to around 1500 F.

3 In the combustion zone the range of temperatures may be from around 500 F. to 1500 F;, depending upon the portion of this zone considered and previous history of the combustion;

' In the condensation zone temperatures may range from 212 F. to around 450 F. depending upon the pressures involved. The temperature is considerably related to the condensation temperature of water under the pressure conditions which exist.

Finally, beyond the condensation zone the temperatures will range downwardly to the original temperature of the reservoir which may be essentially regarded as 70 F. plus the geothermal gradient for the ambient zone.

The problem presented in the treatment of reservoirs of the type more specifically under consideration is the following:

Stemming fundamentally from the high boiling point fractions contained in the petroleum oils, as the combustion zone is propagated through the reservoir, Water and hydrocarbons are vaporized and flow downstream to cooler portions of the formation where the vapors condense and cause the buildup of 'what may be differentiated as three subzones of high oil and/or water saturation. One intermediate subzone having a high Water saturation is in the temperature plateau region 28 of the condensation zone. This subzone has a temperature generally corresponding to the condensation temperature of water under the pressure conditions involved. Preceding this is a first subzone indicated at 30 located in the region of the steep temperature profile between the plateau of the condensation zone and the peak temperature region of the combustion (cracking) zone. Beyond the plateau is another subzone 32 which is in the region between the plateau of the condensation zone and the ambient zone. The particular temperature gradients of the subzones 30 and 32 are dependent upon the distillation characteristics of the crude oil in the formation.

FIGURE 4 diagrams a typical composition which may exist in a reservoir of the type herein particularly considered. The condensation zone represented by the line AB is short, and the liquid line is intercepted at a fairly high temperature. Typically, for example, only four percent of the crude might vaporize below 400 F. and approximately 40% might vaporize below 600 F. This characteristic will cause the buildup of a high oil saturation in subzone 30 amounting to as much as 50% of the cumulative oil.displaced ahead of thecornbustion zone. Such a concentration of oil saturation will produce an oil block in this subzone impeding. the flow of gas, and interfering with the proper *progress of the burning operation.

Further, since only 4% of 'the oil vaporizes below 400 F., the, oil accumulated in subzone 32 will consist largely of virgin crude oil (having high viscosity characteristics) with much less than the desired dilution by the lighter, less viscous fraction of the displaced crude oil. Here again, therefore, there will occur an oil block to the proper and desired flow of gases.

While only a particular example has been assumed in the immediately preceding discussion, the example is fairly typical of 'what is found in reservoirs of the type here under consideration. I

In contrast with the foregoing, let it be assumed that instead of an oil in the reservoir having the characteristics indicated in FIGURE 4 there was an oil having the characteristics indicated in FIGURE 5. characteristics of this latter figure were involved, a desirable performance in a forward in situ combustion process would occur. Here, typically, 95% of the crude might distill below 580 F. and 12% might typically distill below 400 F. Under these conditions there would be less oil saturation in subzone 30 and more dilution of the virgin crude by lighter displaced fractions in subzone 32. t The condensation zone is here represented by CD.

If the last assumed composition was that in the reservoir, the several subzones would be considerably extended If the distillation" 7 content.

as indicated at 28', 30' and 32' in FIGURE 3. (Zones in this figure corresponding to zones in FIGURE 2 are designated by the same numerals primed.) In accordance with the present invention the last mentioned type of composition is effectively secured by injection of hydrocarbons into the wells prior to combustion or, following initial combustion, preceding a subsequent combustion operation.

The injection which is efrected may be considered as if made up of two separate injections, though these injections may be, and generally desirably are, combined or, if separated, desirablyboth are used, though in some circumstances one or the other might be used to the exclusion of the other.

Considering the treatment to avoid or minimize the eiiect of the viscous block in subzone 30, there is injected into the hydrocarbon-bearing reservoir, through one or more of the air injection wells, a slug of low viscosity hydrocarbons having a boiling range of from 350 F. to 650 F., approximately, at the operating pressure of the reservoir. It will be understood that prior to treatment of the reservoir in accordance with the invention, the pressures existing therein will be due to static conditions,

- Whatever they may happen to be. What is of significance,

however, are the pressure conditions which exist or will exist during burning. Then there is a pressure gradient because of the forced inject-ion of air, which may range from atmospheric pressure as high as one pound per foot of depth at the injection point and to a pressure at the production point depending on the oil lifting technique there used. accordingly means the pressure exist-ing thereat during burning. The boiling range of the hydrocarbons used at atmospheric pressure is here not significant; but the choice is made in terms of the boiling range at the operating pressure. The size of this slug may amount, in volume, from 1% to as much as 25% of the volume of petroleum oils boiling above 350 F. (at the operating pressure) in the expected displaced volume of the reservoir, .the amount used depending on the properties ofthe rock and its hydrocarbon content. The viscosity of this slug should be in the region of one centipoise, more or less, at a temperature of 350 F.

To alleviate or prevent the viscous block in subzone 32, there is injected into the hydrocarbon reservoir through one or more of the air injection wells a slug of low viscosity hydrocarbon having a boiling range from F. to 350 F. at the operating pressure of zone 32. The size of this slug should range in volume from about 2% to about 5% of the petroleum in the expected displaced volume of the reservoir, but here again the quantity depends on the properties of the rock audits hydrocarbon The viscosity of this last slug should be in the region of one centipoise, more or less, at a temperature of 100 F.

The compositions of the slugs just mentioned may 'consist of either pure or a wide range of mixtures of paraffinic, aromatic or olefinic type hydrocarbons. However, in practice, economy would dictate that the fluid should consist of raw products obtained in bulk from the distilla- 'tion of crude oil having the boiling temperature ranges specified, the ranges being considered in terms of the operating pressure or pressures of the reservoir zones.

The first fluid, for alleviating the oil block in the subzone 30, may consist of a partially refined hydrocarbon having properties igeneral'ly similar to those of a kerosene or light fuel oil fraction. The second mentioned fluid may consist Operating pressure at a particular zone' much better results and involves additional expense of operation not warranted by the results.

The slugs referred to may be injected into the reservoir either separately or as a mixture. As already noted, one may be introduced without the other, depending upon the conditions which are deduced to exist and which may require remedy for optimum progress of the combustion process.

Usually, it would be desirable to effect injection of the slug or slugs into the reservoir prior to ignition of the formation. This will result in the initiation of the burning operation with the reservoir, in effect, at least in its initial portions containing instead of the original petroleum deposit a composition which in effect is' that illustrated in FIGURE 5.

It may be here noted that the introduced hydrocarbons may not, at the time of introduction, produce any homogeneous composition in the formation; rather, the desired composition may, and usually will be, achieved after some initial burning. Y

The disclosed process may be instigated any time after the combustion zone has progressed beyond the immediate vicinity of the injection well or wells. In fact the two slugs may be injected at different times, for example that of the first mentioned type prior to ignition and that of the second mentioned type after the combustion zone has propagated beyond the vicinity of the injection well or wells. This sequence, however, may be reversed, if desired. The particular injections and their sequences will be determined by consideration of the conditions existing in the particular reservoir as determined from prior corings, production observations, and the like, or may be dictated in accordance with the results observed following some combustion.

When slugs are injected subsequent to ignition, safety precautions should be observed by buffering them from pre-injected air and post-injected air using exhaust gases or other convenient inert gases such as nitrogen or carbon dioxide. This is, of course, to prevent undesired combustion 'and waste of the hydrocarbons. After the slugs 'have been located in the reservoir, either prior to any ignition or subsequent to burnin the forward in situ combustion process may be operated in conventional fashion or in such special fashion as, for example, is disclosed in my application Serial No. 235,028, filed November 2, 1962. In general, the present invention may be looked upon as involving modification of the contents of a reservoir which is to be subjected to the in situ combustion procedure, with the latter carried out in accordance with an optimum program determined by knowledge of the reservoir composition and its dimensions and other physical characteristics.

The effect of the foregoing is a modification of the temperature profile from that illustrated in FIGURE 2 to that illustrated in FIGURE 3. (It will be understood that these profiles are descriptive only and may vary quite considerably from reservoir to reservoir depending upon the characteristics thereof.) Particularly involved is an elongation of the condensation zone. Because of the higher proportion of more volatile constituents resulting from the injected slugs the condensations of the hydrocarbons will be spread out or delayed with more gradual temperature gradients. Dilutions of the original formation contents occur mobilizing the contents and reducing liquid saturation. The apparent liquid-vapor phase diagram will be modified as indicated schematically by the change from FIGURE 4 to FIGURE 5. In particular the liquid line of the liquid-vapor phase envelope is moved toward a region of lower temperature, and the percent liquid curves are distributed over a wider temperature range. In eifect, the condensation zone in view of the dilution is stretched out along the line CD of FIGURE 5. The expansion of the condensation zone reduces liquid saturation, and increases heat transfer toward the ambient zone, also reducing the apparent viscosities of the accumulated liquids.

In summary, application of the forward in situ combustion process may be extended to hydrocarbon-bearing reservoirs containing high boiling range, high viscosity, 'low gravity petroleum oils by use of the process disclosed, whereas without it oil blocks would develop which would impede progress of the combustion, slowing down and/ or rendering uneconomical the combustion process. Effective igas permeability is increased due to reduced liquid saturation, increased heat transfer, and reduced liquid viscosity.

It will be evident that various changes in details of operation may be made without departing from the invention as defined in the following claims.

What is claimed is:

1. The method of production of hydrocarbon materials from a formation containing high viscosity, high boiling point petroleum hydrocarbon deposits, which formation is penetrated by at least two wells, comprising:

injecting through one of said wells into only a portion of said formation nearest that well low viscosity hydrocarbons having as major contents (a) hydrocarbons having a boiling range of approximately 350 F. to 650 F. at the operating elevated pressure of a condensation zone in contemplated later burning of the formation and (b) low viscosity hydrocarbons having a boiling range of approximately F. to 350 F. at the operating elevated pressure of a condensation zone in contemplated later burning of the formation; and

thereafter injecting into said well an oxygen-containing gas and supporting thereby combustion of carbonanaceous material in said formation with continuous progression of the combustion towards the other of said wells and removal of products from the latter, said combustion being carried out under said elevated pressure conditions in the formation.

2. The method according to claim 1 in which the injected hydro-carbons (a) having said boiling range of 350 F. to 650 F. are in an amount in volume ranging from 1% to 25%, approximately, of the volume of petroleum hydrocarbons boiling, at said elevated pressure, above 350 F. in the expected displaced volume of the formation, and in which the injected hydrocarbons (b) having said boiling range of 100 F. to 350 F. are in an amount in volume ranging between 2% and 5%, approximately, of the volume of the hydrocarbons in the expected displaced volume of the formation.

3. The method according to claim 1 in which the injected hydrocarbons (a) having said boiling range of 350 F. to 650 F. have a viscosity not substantially exceeding one centipoise at a temperature of 350 F., and in which the injected hydrocarbons (b) having said boiling range of 100 F. to 350 F. have a viscosity not substantially exceeding one centipoise at a temperature of 100 F.

4. The method according to claim 2 in which the injected hydrocarbons (a) having said boiling range of 350 F. to 650 F. have a viscosity not substantially exceeding one centipoise at a temperature of 350 F., and in which the injected hydrocarbons (b) having said boiling range of 100 F. to 350 F. have a viscosity not substantially exceeding one centipoise at a temperature of 100 F.

5. The method according to claim 1 in which said injected hydrocarbons include aromatic hydrocarbons in amount by volume ranging upwardly to about 0.25% of asphalts, asphaltenes and resins in the petroleum hydrocarbons in the expected displaced volume of the formation.

6. The method of production of hydrocarbon materials from a formation containing high viscosity, high boiling point petroleum hydrocarbon deposits, which formation is penetrated by at least two wells, comprising:

injecting through one of said wells into only a portion of said format-ion nearest that well low viscosity hydrocarbons having as major contents hydrocarbons having a boiling range of approximately 350 F. to 650 F. at the operating elevated pressure of a condensation zone in contemplated later burning of the formation; and

thereafter injecting into said well an oxygen-containing gas and supporting thereby combustion of carbonaceous material in said formation with continuous progression of the combustion toward the other of said Wells and removal of products from the latter, said combustion being carried out under said elevated pressure conditions in the formation.

7. The method accordiugto claim 6 in which the injected hydrocarbons having said boiling range of 350 F. to 650 F. are in an amount in volume ranging from 1% to 25% approximately, of the volume of petroleum hydrocarbons boiling above 350 F. in the expected displaced volume of the formation.

8. The method according to claim 6 in which said injected hydrocarbons include aromatic hydrocarbons in amount by volume ranging upwardly to about 0.25% of asphalts, asphaltenes and resins in the petroleum hydrocarbons in the expected displaced volume of the formation.

9. The method of production of hydrocarbon materials from a formation containing high viscosity, high boiling point petroleum hydrocarbon deposits, which formation is penetrated by at least two wells, comprising: injecting through one of said wells into only a portion of said formation nearest that well low viscosity hydrocarbons having as major contents low viscosity hydrocarbons having a boiling range of approximately 100 F. to 350 F. at the operating elevated pressure of a condensation zone in contemplated later burning of the formation, said injected hydrocarbons having said boiling range of 100 F. to 350 F. being in an amount in volume ranging from 2% to 5%, approximately, of the volume of the hydrocarbons in the expected displaced volume of the formation; and thereafter injecting into said Well an oxygen-containing gas and supporting thereby combustion ofcarbonaceous material in said formation with continuous progression of the combustion towards the other of said wells and removal of products from the latter, said combustion being carried out under said elevated pressure conditions in the formation.

10. The method of production of hydrocarbon materials from a formation containing high viscosity, high boiling point petroleum hydrocarbon deposits, which formation is penetrated by at least two wells, comprising: injecting through one of said wells into only a portion of said formation nearest that well low viscosity hydrocarbons having as major contents low viscosity hydrocarbons having a boiling range of approximately F. to 350 F. at the operating elevated pressure of a condensation zone in contemplated later burning of the formation, said injected hydrocarbons including aromatic hydrocarbons in amount by volume ranging upwardly to about 0.25% of asphalts, asphaltenes and resins in the petroleum hydrocarbons in the expected displaced volume of the formation; and thereafter injecting into said well an oxygen-containing gas and supporting thereby combustion of carbonaceous material in said formation with continuous progression of the combustion towards the other of said wells and removal of products from the latter, said combustion being carried out under said elevated pressure conditions in the formation.

References Cited by the Examiner UNITED STATES PATENTS 2,793,697 5/ 1957 Simm 166-39 2,796,132 6/1957 Bruce 16639 2,863,510 12/1958 Tadema et a] 16639 X 2,871,941 2/1959 Allen et al. 16638 2,889,881 6/1959 Trantham et a1 166-11 3,093,191 6/l963 Glass l66-l1 3,167,121 1/1965 Sharp 166-11 CHARLES E. OCONNELL, Primary Examiner.

BENJAMIN HERSH, Examiner.

S. J. NOVOSAD, Assistant Examiner. 

1. THE METHOD OF PRODUCTION OF HYDROCARBON MATERIALS FROM A FORMATION CONTAINING HIGH VISCOSITY, HIGH BOILING POINT PETROLEUM HYDROCARBONS DEPOSITS, WHICH FORMATION IS PENETRATED BY AT LEAST TWO WELLS, COMPRISING: INJECTING THROUGH ONE OF SAID WELLS INTO ONLY A PORTION OF SAID FORMATION NEAREST THAT WELL LOW VISCOISTY HYDROCARBONS HAVING AS MAJOR CONTENTS (A) HYDROCARBONS HAVING A BOILING RANGE OF APPROXIMATELY 350* F. TO 650* F. AT THE OPERATING ELEVATED PRESSURE OF A CONDENSATION ZONE IN CONTEMPLATED LATER BURNING OF THE FORMATION AND (B) LOW VISCOSITY HYDROCARBONS HAVING A BOILING RANGE OF APPROXIMATELY 100* F. TO 350* F. AT THE OPERATING ELEVATED PRESSURE OF A CONDENSATION ZONE IN CONTEMPLATED LATER BURNING OF THE FORMATION; AND THEREAFTER INJECTING INTO SAID WELL AN OXYGEN-C0NTAINING GAS AND SUPPORTING THEREBY COMBUSTION OF CARBONANACEOUS MATERIAL IN SAID FORMATION WITH CONTINUOUS PROGRESSION OF THE COMBUSTION TOWARDS THE OTHER OF SAID WELLS AND REMOVAL OF PRODUCTS FROM THE LATTER, SAID COMBUSTION BEING CARRIED OUT UNDER SAID ELEVATED PRESSURE CONDITIONS IN THE FORMATION. 